(1) Field of the Invention
The present invention relates to the field of printer assemblies, and more particularly, to an ink jet printer and a method for printing an image having reduced color bleed when printed on common use paper.
(2) Prior Art
Scan-type printer assemblies typically print color images by directly injecting onto a piece of paper the colors that form an image. The image is made up of a number of discrete points which are known as "pixels." In a color image each of the pixels has a color. The color image is rendered into device pixels by either the host computer or the printer controller using various halftoning techniques. The resulting image is made up of pixels at the resolution of the ink jet printer, where each of these pixels represents an individual dot of ink to be projected onto the surface of the paper. The methods for rendering an image are well known in the art. In a typical ink jet printer, a print head ejects ink dots onto the surface of the paper in those locations which correspond to the individual pixels of the color image. A print head typically accesses the different regions of the paper surface by means of moving the sheet of paper by use of a plurality of rollers which are powered by a motor drive. The print head moves across the page by means of a print head drive system. In these prior art printers, the print head typically prints the image exactly as it is relayed to the print head. In other words, the printed image exactly corresponds to the pixel image that was rendered at the device resolution.
A major problem with prior art printers using common paper and printing methods is the fact that colors tend to bleed together at boundaries between regions having different colors.
Bleed between different color regions can be quite severe. The bleed can produce altered color as far within the solid color region as fifty or more pixels (or dots) from the boundary. This problem is particularly acute with the respect to boundaries between two colored regions when both of those colored regions are secondary colors. Prior art methods for eliminating the color bleed problem have included the use of coated paper. Coated paper is undesirable as it is more expensive than so called plain paper. Furthermore, the use of coated paper does not always entirely eliminate the color bleed problem. One way to minimize bleed is to process the print signal which represents the image to be printed so as to produce an altered print image. Prior art techniques for altering print images for reducing color bleed have typically involved the elimination of a row or more of ink dots (or pixels) at the boundary between the two different colored regions. This often produces a white area between the two different regions The problem with this prior art method is the fact that the white area, which is often a line, is visible to the naked eye. Thus, an inferior quality image is produced.
What is needed is an apparatus and method for printing which will allow for reduced bleed between boundary regions, particularly those boundary regions which separate two regions having colors which are secondary colors. This apparatus and method should allow for the use of plain paper and should give a high quality image.